1. Field of the Invention
The present invention relates to a material for an ocular lens (an lens for an eye), in which an ultraviolet absorbing copolymer is used.
2. Description of the Related Art
As ocular lenses, contact lenses and intraocular lenses have conventionally been used for the correction of visual acuity and as a substitute for the eye lens in the operation of cataract, respectively. Base materials for the ocular lens can be classified into several kinds according to their properties. Typical examples of the base material include polymethyl methacrylate (PMMA) which is a not-water-containing type, has a narrow intramolecular space and is rigid and polyhydroxyethyl methacrylate (PHEMA) which is a water-containing type and has a relatively wide intramolecular space. Different from the eye lens, however, neither of them is not able to absorb ultraviolet rays. Various intraocular lenses imparted with ultraviolet absorbing properties have therefore been proposed.
In fact, a benzotriazole ultraviolet absorber has been added to PMMA lens. Although the base material and the ultraviolet absorber are only physically bound each other, a rigid polymer typified by PMMA has an intramolecular space narrow enough not to allow the passage of the ultraviolet absorber. The ultraviolet absorber is therefore not easily eluted from the PMMA lens.
Water-containing type polymers typified by PHEMA or soft materials have a relatively wide intramolecular space so that elution of an ultraviolet absorber having a low molecular weight occurs and the addition of such an absorber does not bring about the desired effect. Several methods have already been disclosed with a view to preventing such a problem. They are however not satisfactory because of a troublesome synthesizing operation, a large amount of elution or insufficient wavelength absorption characteristics.